PROF. SULLY has given us in his latest work a model monograph on laughter.1 With much charm and penetration, and in the light of a wide knowledge of the very extensive literature of the subject, he discusses the nature, causes and effects of laughter, its uses, its origin, its development and its future in the race and in the individual. He criticises the more important of the many theories of the ludicrous propounded by philosophers in all ages; he shows that each one of them fails to account for a considerable proportion of the many varieties of the ludicrous, and he concludes “that the impressions of the laughable cannot be reduced to one or two principles.” While thus recognising the impossibility of bringing all kinds of laughter-causing things under one-formula, Prof. Sully points to two causes of laughter which are closely allied and frequently cooperate, namely a sudden oncoming of gladness and a sudden release from constraint, and these, he regards as the two principles most generally applicable to the explanation of the nature of the ludicrous. There is implied here and throughout the book me assumption that “the laugh is in general an expression of a pleasurable state of feeling,” an assumption which finds also explicit expression in several passages, e.g. “that outburst of gladness which we call laughter” and “laughter being primarily the expression of the fuller measure of the happy or gladsome state.” It is assumed, in fact, that that which makes us laugh does so in general in virtue of its pleasing us, or, more shortly, that in general we laugh because we are pleased.